Esophageal stethoscope

ABSTRACT

An esophageal stethoscope includes a plastic tube having at least one bore extending over the length of the tube. The tube has a distal end which is insertable into the esophagus of the patient, and a proximal end for providing respiratory and heart sounds produced at the distal end and transmitted through the tube for monitoring. A microphone element is mounted in the bore of the tube at the distal end for detecting the respiratory and heart sounds, and providing corresponding electrical signals. The signals are conducted through wires arranged in the tube bore to the proximal end of the tube where the wires are connected to a terminal member. Accordingly, the heart and respiratory sounds can be reproduced with maximal signal to noise ratio when the terminal member is connected to a suitable amplifier and speaker arrangement, or other signal processing equipment.

This is a division of application Ser. No. 267,046, filed May 26, 1981,now U.S. Pat. No. 4,484,583.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to esophageal stethoscopes, andspecifially to an esophageal stethoscope including a microphone elementat its distal end for detecting heart and respiratory sounds produced bya patient when the stethoscope is inserted into the patient's esophagus.

2. Description of the Prior Art

Conventional esophageal stethoscopes include a length of plastic tubingone end of which, the distal end, may have a number of openings formedthrough the tube wall and a relatively thin protective covering sealedover the openings to prevent body fluids from entering the tube when thedistal end is inserted into a patient's esophagus. The other end of thetube, i.e., the proximal end, may be connected to a fitting such as a"Luer" type of fitting for connecting with a set of stethoscopeearpieces.

Esophageal stethoscopes are often used by anesthesiologists who listento the heart and respiratory sounds of a patient during the course of asurgical procedure. The anesthesiologist listens for changes in theheart or respiratory sounds which serve to indicate the existence of aproblem requiring the immediate attention of the anesthesiologist. Inthe event the anesthesiologist must be located a considerable distancefrom the patient during a surgical or other operating procedure, it willbe understood that the length of the stethoscope tubing must becorrespondingly increased in order that it remain connected with thestethoscope earpieces which must always be worn by the anesthesiologist.However, as the length of the tubing is increased, the intensity of thesounds reaching the proximal end of the tubing diminishes accordingly.Further, there are instances when the anesthesiologist must move aboutthe operating room to attend to required tasks. This requires that thetubing be temporarily disconnected from the stethoscope earpieces, sothat the patient's heart and respiratory sounds are not monitored duringsuch times. This presents a potential hazard for the patient.

It is also known to provide a microphone at one end of a length offlexible tubing so as to convert heart sounds picked up by a chest pieceat the other end of the tubing into electrical impulses. For example,U.S. Pat. No. 2,699,465 issued Jan. 11, 1955, to S. Hamilton shows suchan arrangement which is used in a warning system for indicating thecessation of cardiac funtions. Another device is also known in which theproximal end of an esophageal stethoscope is provided with a Luerfitting for coupling with a microphone of an FM transmitter, therebyallowing sounds conveyed to the proximal end of the tubing to bemonitored by a receiver at a location remote from the operating table.

It will be appreciated, however, that the placement of a microphone atthe proximal end of a stethoscope tube will result in the detection andreproduction of sounds developed over the entire length of the tubewhich sounds may not be among those desired to be heard. For example,bending movement of the stethoscope tube will produce noises at theproximal end of the tube and, since the microphone is unable todiscriminate between these noises and the respiratory and heart soundsoriginating from the distal end of the tube, these noises will beconverted into electrical signals thus making the monitoring of theheart and breathing sounds more difficult.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome the above and othershortcomings in the known esophageal stethoscopes.

Another object of the invention is to provide an esophageal stethoscopewhich provides a relatively high signal to noise ratio where the desiredsignal corresponds to a patient's heart and breathing sounds against thebackground of all other physiologically and environmentally producednoise.

Another object of the invention is to provide a stethoscope in whichdistortion of the heart and breathing sounds resulting from tubinglength, diameter or flexure is virtually non-existent.

Another object of the invention is to provide an esophageal stethoscopehaving high sensitivity such as to allow monitoring of heart andbreathing sounds produced at its distal end, which sounds have notheretofore been made audible, at the proximal end of the stethoscope.

Another object of the invention is to provide an esophageal stethoscopehaving high noise immunity, thereby being much less susceptible to audiointerference normally encountered with the conventional stethoscopeswhen the tubing is physically disturbed or contacted.

In accordance with the present invention, an esophageal stethoscopeincludes a plastic tube having at least one bore extending over itslength, a distal end for insertion in the esophagus of a patient and aproximal end for providing breath and heart sounds produced in thevicinity of the distal end for monitoring. An audio transducer elementis mounted in the bore of the tube at the distal end for detecting thebreath and heart sounds and providing corresponding electrical signals.Means arranged in the bore and coupled to the microphone element operateto conduct the microphone signals to the proximal end of the tube, andterminal means coupled to the conducting means at the proximal end ofthe tube provides the microphone signals for further processing.

The esophageal stethoscope of the present invention is particularlyadvantageous because it not only provides high quality reproduction ofthe actual heart and breath sounds, but also, the sounds are reproducedfree from interference by extraneous noise caused by the physical makeup of the stethoscope. Additionally, one can obtain equally excellentresults regardless of whether 12, 18 or 24 Fr. diameter tubing is used.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the drawings and descriptive matter in whichthere are illustrated and described preferred embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a perspective, fragmented view of an esophageal stethoscopeaccording to the invention;

FIG. 2 is a schematic diagram showing a test measurement system forevaluating the performance of the esophageal stethoscope of FIG. 1; and

FIG. 3 is a sectional view of one form of plastic tubing which can beused for the stethoscope of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a perspective view of an esophageal stethoscope according tothe invention. Basically, the stethoscope 10 includes a length ofplastic tubing 12 which can be of any of the conventional types oftubing used for esophageal stethoscopes such as, for example, tubingsold under the trade name "Silastic" by Dow Corning Corporation. Tubing12 has an axial bore 14 extending over its length between a distal end16 which is insertable into a patient's esophagus, and a proximal end 18opposite the distal end 16 whereat breath and heart sounds produced inthe vicinity of the distal end can be monitored, as explained below.

The distal end 16 of the tubing 12 has a number of acoustic openings 20through the wall of the tubing 12 to enable sounds to enter within thebore 14 of the tube 12 at the distal end 16. A relatively thin wallprotective cap 22 is provided over the distal end of the tube 12 tocover the acoustic openings 20 and thus prevent body fluids fromentering within the tube bore 14. Cap 22 may be the same type of capprovided at the distal end of a conventional esophageal stethoscope, andcan be sealed at the distal end 16 of the tube 12 with conventionalbonding techniques, e.g., heat bonding, high frequency treatment, or PVCglue or similar adhesive.

An audio transducer element 24 is mounted at the distal end 16 of thetube bore 14 and can be fixed in position by way of a force fit withinthe tube wall. This audio transducer element can be any type of devicewhich can sense the audio input from the heart and breath sound andconvert them to corresponding electrical signals, e.g., a microphone,pressure transducer or the fiber optic embodiment described hereinafter.For purposes of simplification, element 24 will hereinafter be discussedin terms of a microphone element. If necessary, microphone element 24can be further supported with silicone adhesive deposited only along theedges of the element 24 in an amount just sufficient to preventmovement. One type of microphone element 24 which has been used is ModelNo. EA 1934, manufactured by Knowles Electronics Inc. of Franklin Park,Ill. This element is an electret type, but a ceramic type such as ModelNo. BL 1785 of the same manufacturer can also be used. The latter modelhas a frequency range of from 20 to 10,000 Hertz with a nominalsensitivity at 1000 Hertz of -69 dB relative to one volt per microbar.

At the proximal end 18 of tube 12 there is provided a T connector 26having a branch 28 fitted at the proximal end of tube 12 to communicatewith the bore 14. A conventional electrical connector 30 is fitted on asecond branch 32 of the T connector 26. A pair of wire leads 34 isrouted through the tube bore 14, the leads 34 being connected at thedistal end 16 to the microphone element 24. The leads 34 are connectedat the proximal end 18 to the electrical connector 30 so that signalsprovided by the microphone element 24 and conducted by the leads 34through the tube 10 are made available for further processing at theconnector 30.

A third branch 38 of the T connector 26 is coupled through a shortlength of tubing 40 to a conventional Luer connector 42. Thisarrangement allows audible sounds conducted through the tube bore 14from the distal end 16 of the tube to be monitored with a set ofconventional stethoscope earpieces when the earpieces are connected tothe Luer connector 42. Accordingly, the present stethoscope 10 allowsfor monitoring of a patient's heart and breath sounds either by way ofequipment which audibly reproduces the sounds in response to theelectrical signals provided by the microphone element 24 at theconnector 30, or with the aid of a conventional set of stethoscopeearpieces when coupled to the Luer connector 42. This feature isimportant in that should the microphone element 24 or other audiocomponents fail during the course of an operating procedure on apatient, the patient's heart and breath sounds can still be monitored bycoupling stethoscope earpieces to the Luer connector 42.

FIG. 3 shows a modification of tube 12 in FIG. 1 wherein a tube 50 of"Silastic" silicone material is provided, the tube 50 having a firstbore 52 for audibly conducting the heart and breath sounds produced atthe distal end 16 to the proximal end 18 of the tube 50, and secondbores 54 for containing the wire leads 34 and routing the leads 34between the microphone element 24 (not shown) and the electricalconnector 30 (not shown), similar to the arrangement of FIG. 1.Preferably, the cross-section of the second bores 54 should be justsufficient to prevent the wire leads 34 from moving relative to the tube50, so that audible noise originating from the wire leads themselveswill be suppressed when the tube 50 is flexed as often occurs duringuse. It is also possible in this case for leads 34 to be moldedseparately into the wall of tube 50. Such noise originating frommovement of the leads 34 relative to the interior of the tube 50 wouldotherwise be heard when a set of stethoscope earpieces is coupled ontothe Luer connector 42. Tubing having a cross-section similar to that oftube 50 is also known and may be obtained from Dow Corning Corporationunder the "SILASTIC" name.

FIG. 2 shows an arrangement for measuring the performance of the presentstethoscope 10 relative to the conventional esophageal stethoscope inwhich a microphone element is placed at the proximal, rather than thedistal end of the stethoscope 10. The present stethoscope 10 and acomparison stethoscope 10' having a microphone element 24' at itsproximal end were inserted together in the esophagus of a dog 100. Theoutputs of both microphones 24,24' were connected through identicalcables 110 to a coupler device 112 which provided a 9-volt DC supply toboth microphone elements 24,24' while simultaneously AC coupling themicrophone elements 24,24' to a two-channel tape recorder 114.Accordingly, the signals provided by both microphone elements 24,24'were simultaneously recorded on tape. The outputs from the tape recorderwere coupled to a conventional high-fidelity stereo amplifier 116, andthe speaker outputs of the amplifier 116 were connected to a channelswitch 118. Switch 118 was arranged to allow switching of either speakeroutput of the amplifiar 116 to a single speaker 120 for instantaneouscomparison.

As measured on the tape recorder level meters, the signals from themicrophone element 24 of the present stethoscope 10 were 34 db higherthan the signals provided simultaneously by the microphone element 24'of the comparison stethoscope 10'.

The present stethoscope 10 provides an extended frequency responsewhich, if a microphone element such as type 1785, mentioned above, isused, can be as wide as from 20 Hz to over 10 kHz. The heart and breathsounds are transduced at the location of the heart and electricallytransmitted through wires to an amplifier or other electrical signalprocessing equipment. Therefore, these sounds are not subject to theinherent attenuation due to the length, diameter or flexibility of thestethoscope tube.

With the recent trend toward the use of disposable medical devices, thepresent stethoscope 10 may be constructed in a disposable form which iseconomically feasible. Microphone element 24 may, for example, be platedor otherwise deposited at the distal end of the tube 12 (or 50) duringthe manufacturing process of forming the stethoscope tube. It is alsopossible to use an optic fiber in place of the wire leads 34 and allowthe sound pressures developed at the distal end of the stethoscope tocause a thin diaphragm membrane to vibrate, and thereby modulate a beamof light directed toward the distal end of the optic fiber from alight-emitting diode mounted in the tube or a conventional fiber opticlight source external to the stethoscope.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the inventiveprinciples, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:
 1. An esophageal stethoscope comprising a flexibleplastic tube of a particular length and having a first bore extendingover said length, said tube having a distal end for insertion in theesophagus of a patient and a proximal end opposite said distal endwherein said first bore audibly conducts breath and heart soundsproduced in the vicinity of said distal end through said tube formonitoring at said proximal end, an audio transducer element mounted atsaid distal end of said tube for detecting the breath and heart soundsand providing output signals representative of the breath and heartsounds as produced only in the vicinity of said distal end, said audiotransducer element being arranged in said tube so that said outputsignals are substantially unaffected by vibrations produced over thelength of said tube outside the vicinity of said distal end, terminalmeans at the proximal end of said tube for providing said output signalsfor further processing, connecting means arranged in said tube andcoupled to said audio transducer element for connecting said audiotransducer element to said terminal means, and fitting meanscommunicating with said first bore of said tube at said proximal end forenabling the heart and breath sounds audibly conducted by said firstbore to be monitored by a stethoscope earpiece and wherein said audiotransducer element includes a thin membrane which vibrates in responseto sound pressure corresponding to the breath and heart sounds and alight emitting diode means for providing a light beam to be modulated bysaid membrane, and said connecting means includes an optic fiber meansextending over the length of said tube for conducting the modulatedlight beam from the distal end of said tube to said terminal means atthe proximal end of said tube.
 2. An esophageal stethoscope according toclaim 1, including means coupled to said terminal means for audiblyreproducing the heart and breath sounds in response to said signals.